Voice current amplifier for long distance telephone lines



Aprifi 2E L. E. ADLER 1,996,267

VOICE CURRENT AMPLIFIER FOR LONG DISTANCE TELEPHONE LINES Filed March a, 1931 2 Sheets-Sheet 1 Qwucntoz 1.66 f. fla /er" r, j I 1 a5,

VOICE CURRENT AMPLIFIER FOR LONG DISTANCE TELEPHONE LINES Filed March 6, 1931 2 Sheets-Sheet 2 glwvemtoz Patented Apr. 2, 1935 UNITED STATES VOICE CURRENT AMPLIFIER FOR LONG DISTANCE TELEPHONE LINES I LeeEfAdler, Dallas; Tex. Application March 6, 1931, Serial No. 520,606 7 1 9 Claims. (01. 179-170) This invention relates to new and useful im provements in voice current amplifiers for long distance telephone lines.

One object-of the invention'is to provide improved means for increasing or amplifying the volume of sound transmission in'both directions on long distance telephonelines without the use of batteries, motor-generator sets-or other expensive and cumbersome equipment.

Another object of the invention is to provide a voice current amplifier which is simple and easy to install, is inexpensiveto maintain and operate,

provides an adequate amountof volume increase, has the ability to perform properly atall times and on multi-party lines, and is complete in itself without the need of additional balancing equipment and other auxiliary accessories;

A further object of the invention is to provide a variable stabilizer for balancing the impedance and likewise the volumeincrease on theopposite ends of the talking line, whereby the amplifier may be balanced against any type or length of line to obtain a uniform amount of volume increase despite variations in line impedance.

A still further object of the invention is to provide means for holdingthe primary or moving circuit open except during the actual period of ringing by either operator, whereby current consumption and wear on the ringing machine or source of ringing current is reduced to a minimum and efiicient maintenance of the device is set up.

An important object of the invention is to provide means for automatically connecting or disconnecting the amplifying ap-paratus in or from the telephone circuit when said amplifier is in an operative or inoperative condition.

Another object of the invention is to provide an amplifier which will operate under a greater diiference in line impedances than heretofore possible, together with means for inserting an artificial line or non-inductive resistance in series with the talking circuit of each intermediate bridged station in a party line, whereb'y'the cutting in and the cutting out'of thejintermediate stations by removal'and replacing of the 'receivers will not affect the impedance balance of the line, thus making forsatisfactory long distance amplification on party lines.

Still another'object of the invention is to provide along distance telephone amplifying apparatus with the parts so constructed and arranged in units as to permit the various units to be easily disconnected for removal or renewal.

A construction designed to carry out the in vention will be hereinafter described together with other features of the invention.

The invention will be more readily'understood from a reading of thefollowing'specification and by reference to the accompanying drawings in 5 which an example of the invention is shown, and wherein: a

Figure 1 is a wiring diagram of the line, and stabilizer unit, v i I Figure 2 is a wiring diagram of the amplifier 10 unit and power supply unit, and

Figure 3 is a wiring diagram illustrating th amplifier connected ina long" distance telephone line having intermediate bridged stations.

In-the drawings the numeral l0 designates a 15 connectingblock'by which the amplifier is connected to one end A (Figure 3) of a long dis; 'tance telephone line which needs transmission amplification to increase the volume of sound suflicient for commercially good talking. "The 20 other end B of the telephone line is connected to a connecting block I l. Wire 'leads'Al and A2 connect the block 10' with a repeating coil ,0. This coil is merely an insulating transformer for i reducing line noise or induction and is not a '25 necessary part of the system, when a similar coil is installed in the line ahead of the amplifier for superimposing a telegraph circuit on the talking circuit, as has long been a standard practice. i Y, 1

Wires Cl and C2 lead'ifrom the coil to switch arms Da and Db of a relay D.- This'relayprovides an automatic cut-outorby-pass of-the amplifier in case of failure of the power source supplying the amplifier. The coil of this relay 35 has one end connected 'to a ground leadDl and the other end connected by a'wire lead D2 tora 24 volt contact Ea of a multi-plug. socket E. The

connection of this socket with the power supply unitwill hereinafter be described. I

A manualcutout switch I2 is connected in the lead D2. When the relay D is not operated the switch arms 'Da and Dbv are engaged with contacts Dal and Dbl which have leads Duo and 'Dbd respectively to contacts Dcl and Ddl of the relay D. These latter contacts .are engaged, byiswitch arms D0 and Dd which'are connected by leads Fl and F2 to a repeating'coil F. The coil F has lead connections" BI and B2 to the connecting blockfl l Therefore, when the source of power supply to the amplifier is cutoff the talking circuit is from the A end of the line through the coil C, relay D and coil F to the B end of the line. When a call comes from the B endof the line the circuit is reversed. When the I repeating coils C and F are a part of the amplifier, a simplex leg or telegraph circuit may be superimposed on the talking circuit over leads C3 and F3 which tap the center of the coils. These leads are attached to a connecting block "5 for connection to the telegraph circuit.

When the relay D is energized the switch arms Da, Db, Dc and Dd are actuated into engagement with contactsDaZ, Db2, D02 andDdZ. The contacts D62. and DM have leads Dag and Dbg respectively to switch arms Ga and Gb of a relay G. This relay is normally de-energized with the switch arms Ga and GD engaging contacts Gal and Gbl. These contacts have leads GaH and GbH to the opposite ends of the coil of a relay H. The leads Gal-I and GbH are also connected by leads GHI and GH2 to contacts Ka and Kb of a multi-plug socket K.

When the relay H is energized switch arms Ha and Hb are actuated into engagement with contacts HI and'H2. These contacts are com nected by a common-"lead Hi2 to'the power supply lead D2 and theswitch arms Ha and I-Ib have 'acommon lead Hab' to one end of the coil of a normally de-energized relay L. The other end of the" coil has a ground lead Ll. When the relay L is energized switch arms La and Lb are actuated into engagement with contacts La! and Lbl. These contacts are connected by wire leads and M to a connecting block 43 which is connected with a telephone ringing machine i5 (Figured) at the location of the amplifier. The switch arms La and Lb have leads MD and LbD respectively to the contacts D02 and D 32 of the relay D.

A connecting block H, as shown in FigureB, is' connected in series in the power circuit X- of the ringing machine for normally interrupting said circuit. The block has leads L5 and L6 respectively to a contactLcl anda normally unactuated switch arm Lcof the relay L, whereby the operation of the relay will actuate the switch arm into engagement with the contact and complete the power circuit to the machine thus operating the same. As the relay L is only operatedwhen the A operator rings on the line,

7 the ringing machine is likewise only operated during the period of ringing.

Therefore, when the operator at the A end of the telephone line rings on the line to call the operator on the B end'of the line, the ringing current passesthroughthe repeating coil C, the energized relay D and the de-energized relay G to the coil of relay H, thereby energizing said coil and closing an electric circuit from the power supply lead D2 to the coil of the relay L, thereby energizing the same.v The operation of relay L causes a second ringing current to pass from the ringingmachine l5 through the connecting block I3, the relay L, the relay D and the repeating coil F to the B end of the line for signalling the B operator.

The path of the voice current from A'to B is through the connecting block ID, coil C, relay D and relay G-to the coil of relay H; but as the relay H is of the low fr'equencytype designed to respond only to ringing currents of sixteen cycles and upward, the voice current will not energize and operate said relay. The voice current continues past therelay over leads Ghl and GM to the contacts Ka and Kb of the inu'lti plug K. These This transformer is of the standard three windin; typeand. takes. the place of the more expensive and complicated five winding hybrid coil heretofore used in telephone repeaters.

A winding Me of this transformer and the terminal Mb have leads M3 and M4 to contacts K and Kg of the multi-plug K. These contacts have leads K6 and K! to a repeating coil W. This coil is connected by leads W! and W2 respectively to a variable condenser WA and a variable rheostat WB. The coil, variable condenser and variable rheostat provide an adjustable stabilizer control for setting up a variable impedance in the transformer coil Mo to match or balance the impedance in the coil By this means the amplifier may be balanced against impedance variations in telephone lines of various lengths, whereby a uniform amount of volume gain may be obtained in both directions and singing, howling and oscillation of the vacuum tubes is eliminated.

The windings Ma and Me of the transformer M have a common lead MI and the terminal Mb has a lead M2 to a potentiometer N. This potentiometer is for the purpose of controlling the volume of voice current passing therethrough over leads NI andNZ to the winding 0a of an input transformer 0. If excessive line noise prevails from high-tension line induction or other causes an interference eliminator (not shown) may be plugged in a socket P connected in the leads MI and M2, as shown in dotted lines in Figure 2. r

A winding Ob of the transformer O has a lead OI to the grid terminal Qd of a vacuum tube Q.

This vacuum tube is of the heater cathode type. A by-pass condenser 00 is connected across the winding Ob to-restrict the passage of currents having a higher frequency than required for intelligible voice currents. The cathode Q7) of the vacuum tube has a common lead Q5 to a condenser Q0 and a resistor QOA. The resistor, the condenser and the winding Ob of the transformer 0 have a common ground lead Q01. The purpose of the resistor is to make the ground of the amplifier unit negative to the winding Ob of the transformer 0 instead of neutral, thereby eliminating the need of the C or grid bias battery. This completes the input circuit up to and including the grid circuit of the vacuum tube Q.

A heater or filament Qd of the tube has leads Q5 and Q6 to contacts Kai and Kit of the multiplug K. The contacts in turn have leads Km and Kl to contacts E0 and Ed of the power unit multiplug E, whereby an electric current is supplied to the filament for heating the tube, will hereinafter be explained,

A plate Q0 of the tube has a lead Q2 to a tube testing key R. An ammeter AM is connected to the key by leads AMI and AMZ, and a voltmeter VM having a ground lead ml is also connected to the key by a lead VM2. The key has a lead R1 to a choke coil S which is connected with a grounded reservoir condenser T. This condenser accumulates a volt storage charge. The choke coil has a lead SI to a contact Kc of the multi-plug K, which contact has a lead K3 to a 135 volt contact Eb of the multi-plug socket E. The connection of this socket to the power supply unit will be hereinafter described.

A lead Q3 from the cathode Qb and a lead from the plate Q0 of the tube connect the oathode and plate respectively with the winding Uni of a transformer U. An output condenser QU is connected in the lead Q4. One end of a winding Ua and a terminal UT) of the transformer U have leads K4 and K5 respectively to contacts Kd and Ke of the multi-plug K; These contacts are connected by leads VLI and VL2 to the opposite ends of the coil of a normally de-energized relay V. The leads VLl and VL2 are also connected by leads VLa and VLb to contacts Lct2 and LM of the relay L. This completes the talking circuit from the A to the B ends of the line.

As hereinbeforeexplained the voice current bypasses the relay H and continues throughrthe .multi-plug K and the out-put transformerwinding Ma tothe input transformer 0 where the voltage is raised. The voice currents then pass from the transformer O to the grid Qa of the vacuum tube Q. The voice currents, being of a rapidly varying frequency, set up amplified variations of similar frequencies in the plate Q0 of the tube. These amplified voice currents, being barred from passing through the choke coil S by the impedance ofiered thereby, pass over the lead Q4 through the output condenser vQU and the transformer Ud to the cathode Qb of the tube, thus completing the amplified voice current plate circuit. I

This amplified reproduction of the voice currents passes by induction from the winding Ud of the transformer U to the winding Ua and from said winding over leads K4 and K5, VLI and VL2, to the winding of the relay V. The voice current then passes over leads VLa and VLb and through the'unactuated switch arms La and Lb ofthe relay L and. over leads LaD and LbD to the actuated switch arms Do and Db of the relay D. From the relay D the current passes over leads Fl and F2, through the repeating coil .F and over leads Bi and B2 to the connecting block H and B end of the line. This completes the talking or voice current path from the A end of the telephone line to the B end of said line. 7

When an operator at the B 'end of the line rings an operator at the A end of the line, the ringing current passes through the amplifier in the opposite direction, to that of when the A operator rings, but in the same sequence of operation. The ringing current passes through the connecting block H and the repeating coil F to the relay D. If the relay D is not ener- 1 gized the ringing current will pass from the switch arms Do and Dd over leads Dao and Dbd to the switch arms Da and Db .of said relay and from the latter switch arms through the repeating coil C to the connecting block 10 and A end of the line.

If the relay D is energized the ringing current will pass from the relay switch arms-Dc and Dd through leads LaD and LbD, the deenergized relay L and leads VLa and VLb to the winding of the relay V, thus energizing and operating the same. This relay is similar to the relay'I-I and when'operated has switch arms Va and Vb engaged with contacts Vi and V2. These contacts are connected by a common lead VIZ to the power supply Iead'DZ and .the switch arms have a common lead Vabto oneend of the coil of the relay G. The other end of this coil has a ground lead GI. When the relay G is operated the switch arms Ga and G2) are actuated into engagement with contacts G112 and G122. These contacts are connected to the leads L3 and L6 of the ringing machine l5. Therefore,

when the relay V is operated an'electric circuit is closed to the relay G to operate the same, whereby the second ringing current will pass from the ringing machine through the connecting block I 6, leads L3 and L4, the relay G, the relay D and therepeatingcoil C to the connecting block H] and A end of the line. L

The path of the voice current from B to A is thesame as the path of the ringing current up to the relay V, but as the relay V will only respondto high frequency currents the relay V is not operated and the voice currents. pass through the leads .VLI and VL2, the contacts Kd andKe of the multi-plug K, and the leads K4 andKS to the winding Ua and the terminal Ub of the output transformer U. The impedance of the voice currents in the winding Ua are balanced by a corresponding impedance which is set up in a Winding Uc through leads U3 and U4 which connect said winding and the terminal Ub respectively to multi-plug contacts Kh and Ki. leads K8 and K9 to a repeating coil X similar to the coil W. This coil has leads XI and X2 respectively to a variable condenser XA and a variable rheostat XB, which coil, condenser and rheostat comprise an adjustable stabilizer controL; as hereinbefore explained.

The. balanced voice currents pass from the transformer U over leads UI andUZ to a potentiometer BN which controls the volume of voice currents passing therethrough over leads BNI and BN2 to the winding a of an in:- put transformer 30.. If excessive line noise prevails, an interference eliminator (not shown) These contacts are connected by may be plugged in a socket BP (shown in dotted lines) connected in the leads UI and U2. The voice currents pass by induction to the winding BOb, where the voltage is raised, and from said winding over a lead BO! to the grid BQa of a vacuum tube BQ, similar to the tube Q. A filament 136211 of the tubeis connected-by leads BQE and BQS to'the leads Q5 and Q6, whereby an electric current is suppliedto said'filament for heating the tube. The winding BOb has a by-pass condenser B00, similar to the condenser 00. connected thereacross. The voice currents pass from the grid through the cathode BQb, a lead BQi, a condenser BQO, aresistor BQOA and a ground lead BQOI 'to the ground side of the winding BOb.

:The voice currents passing. through the grid and cathode of the tube set up amplified voice currents in a plate BQc of the tube which plate receives a 135 volt charge through a lead BQZ, testing key BR, lead BR! and choke coil BS from a grounded storage reservoir condenser BT. The coil is connected to the power lead SI. The amplified voice currents pass from the plate. BQc through a lead BQ4, and an output condenser BQU to a winding Md of the output transformer M. From the winding the voice currents pass through a lead BQ3 backtothe cathode BQb, thus completing the amplified voice current plate circuit.- i

The amplified voice currents travellingthrough relay From relayG. the voice currents pass a I through leads DbG and nae, relay. D and repeating coilC to the connecting block I0 andA end of the line. 3

The power-supply unit consistsof a transformer Y which has its primary .winding'Ya connected byleads YAI and YA2 to a plug l8:for connection in a 110 volt, 60 cycle, single phase. power circuit (not shown).

Where a direct current-power cir..-'

.cult only is available, a suitable converter (not shown) may be employed to change the power circuit as desired. The transformer has three 'secondary'windings Yb, Y and Yd. The ends of the winding Yb have leads Ybl and Yb2 to the plates Za and Zb of a rectifying tube Z for supplying200 to 250 volt alternating current to said tube. .The ends of the winding Yc have leads Ycl and Yc2 to the tube filament Zc. In this manner both sets of current alternations are rectilled through the action of the vacuum tube, thereby producing what is generally termed full wave rectification, which results in a pulsating direct current potential between center tap leads Yb3 and1Yc3 respectively of the windings Yb and Ye.

These leads conduct this pulsating current to the negative and the positive ends of a voltage divider resistance Ybc with the positive current passing through filter choke coils YA and YB which are connected in the lead YcS. A plurality of condensers YC, YD and YE having leads YCI and YC2, YDI and Y'DZ, and YE! and YE'Z are bridged intermediate the leads Yb3 and Yc3 on opposite sides of and intermediate the coils YA andYB. These condensers and filter choke coils serve to modulate or equalize the pulsations of the rectified current into a smooth and constant uni-directional current.

A lead Ybci connects the negative end of the voltage divider Ybc to a ground contact E6 of the multi-plug E. This contact has a common ground lead EK to a ground terminal IQ of the line and stabilizer unit and to a ground contact KL of the multi-plug K. A lead Ybc2 connects a 135 volt contact on the voltage divider Ybc to the contact Eb of the multi-plug E for supplying a 135 volt current over .the leads K3 and Si to the amplifying unit, as hereinbefore described. A condenser YF is bridged between the leads Ybcl and Ybc2 to serve as a reservoir and to eliminate any possible remaining hum in the circuit. A lead Ybc3 connects a 24 volt contact on the voltage divider to the contact Ea of the multi-plug E for supplying a 24 volt current to the lead D2 for operating the relays of the stabilizing unit as hereinbefore described.

i The secondary winding Yd of the transformer Y has leads Ydl and YcZZ to contacts E0 and Ed of the multi-plug E for supplying electrical current through the leads KM and KI I, Q5 and Q5, andBQ5 and BQB to the filaments of the tubes in the amplifying unit, as hereinbefore described. If desired, an adjustable rheostat YG may be connected in seriesin the tube filament circuit for conveniently adjusting the voltage to the quantity required by the tubes. Spare contacts E and Er: are provided on the multi-plug E for connection between the amplifier and power units when fPentode or other more-complex types of tubes are employed in the amplifying unit. Any desired voltage may be obtained for such tubes by means of adjustable contacts on the voltage divider. Ybc. a i

In long distance amplification on lines having intermediate bridged stations or party lines the impedance balance of the line is disturbed by the cutting in and out of the intermediate stations, thereby affecting the amplifications. This disturbance is minimized by connecting an artificial line or non-inductive resistance i1 (Figure 3) in series with the talking circuit of each bridged station. The amount or value of this non-inductive resistance is governed by the impedance of the line between the station and the amplifier.

' 'It is obvious that with this device an adequate and uniform amount of volume increase in speech transmission amplification may be had in both directions and at all times on single or multiparty lines of any type or length. Furthermore, the construction and arrangement of the parts in various units make for convenience in repair, removal or renewal and for simplicity and efficiency in installation, maintenance and operation.

Various changes in the size and shape of the different parts, as well as modifications and alterations, may be made within the scope of the appended claims.

Having illustrated and described a preferred form of the invention, what I claim, is:

' i. In a circuit amplifier for long distance telephone circuits, means adapted to be connected at an intermediate point in the telephone line circuit between stations including a stabilizing unit for balancing the amplifier against impedances of the telephone circuit, a two-way amplifying unit, and an A. C. power pack unit for supplying a local source of electrical current for the operation thereof.

2. In a telephone circuit, a circuit amplifying device adapted to be connected in the telephone line circuit intermediate its ends, a power unit for supplying operating current to the amplifier device, and means for bridging the amplifying device and connecting the telephone circuit straight through in case the power unit fails to supply the required operating current to the amplifier.

3. In a telephone circuit, a circuit amplifying device adapted to be connected in the telephone line circuit intermediate its ends, a power unit for supplying operating current to the amplifier device, and means for bridging the amplifying device and connecting the telephone circuit straight through in case the power unit fails comprising a relay operated from the power unit for automatically restoring the amplifier in the telephone circuit when the source of power from the power unit is restored.

4. In a circuit amplifier for long distance telephone circuits, means adapted to be connected at an intermediate point in the telephone line circuit between stations including a stabilizing unit for balancing the amplifier against impedances of the telephone circuit, a two-way amplifying unit, an A. C. power pack unit for supplying a local source of electrical current for the operation thereof, a ringing unit for supplying a source of ringing current to lines on either one or the other side of the amplifier set, and means for rendering current to the amplifier, and the various units phone circuits adapted to be connected in the gizing said elements, and adjustable means for balancing the line impedances. I

'7. A circuit .amplifier as set forth in claim 6, with means for controlling the volume of amplification. g

8. A circuit amplifier as set forth in claim 6, with means for connecting a ringing unit for supplying a local source of ringing current in the circuit at the amplifier, and means for normally rendering said unit inoperative except during the period of ringing through the amplifier set.

9. The combination with a long distance telephone circuit having intermediate bridged stations, of a circuit amplifier adapted to be connected in said circuit at a point intermediate the ends of the circuit, and including means for balancing the amplifier against line impedances, and means connected in series with the circuit of each intermediate bridged station for maintaining the impedance balance of the line when said intermediate stations are cut in or out of the circuit.

10. In a circuit amplifier for long distance telephone circuits, an amplifier adapted to be connected in a telephone circuit, means for balancing the amplifier against impedances of the circuit, means for controlling the volume of the amplifier, a local source of electrical current for supplying the amplifier, and means operated by said local sourceof electrical current for automatically disconnecting the amplifier from the telephone circuit when the local source of electrical current fails and for automatically connecting said amplifier back in the telephone circuit when the local source of current is restored.

11. A circuit amplifier as set forth in claim 10, with means for automatically connecting a local source of ringing current in the telephone circuit,

said means being normally disconnected from said circuit.

12. An amplifier as set forth in claim 10, with meansfor restricting the passage through the amplifierof currents having a higher frequency.

than required for intelligible voice-currents.

13. An amplifier as set forth in claim 10, with means for transposing the local source of electrical current into a smooth, non-pulsating unidirectional current comprising a transformer power pack, rectifyingand filtering devices.

14. An amplifier unit for long distance teletelephone line circuit intermediate its ends including, a stabilizing unit having adjustable means for balancing line impedances, .an amplify- I ing unit having means for controlling the volume, and an A. C. operated power unit with a rectifier and filter for supplying a local source of a substantially non-fluctuating uni-directional current to the amplifier unit.

15. In a circuit amplifier for long distance telephone circuits, a voice current amplifying element, means for supplying a source of power current thereto, means operated by the current supply means for automatically disconnecting the amplifier from the telephone circuit when the current supply means fails and for automatically connecting the amplifier back in the telephone circuit when the current supply is restored, and

normally inoperative means for supplyinga local source of ringing current to the telephone circuit but rendered operative duringa ringing period of a telephone set connected with the telephone power pack, rectifying and filtering devices, and

means in the amplifier set for eliminating the A. C. hum of the power unit.

17. A two-way amplifier set for long distance telephone circuits operable from an A. C. power pack unit as a local source for electric power current for the operation thereof with means in said amplifier set'for eliminatingthe A. C. hum

of the power unit.

18. A two-way amplifier set forlong distance telephone circuits operable from anA. C. power pack unit as a local source for electric power cur- 

